This invention relates to a process for making macromolecular monomers ("macromers" for brevity) of polylactones having an acryloyl or methacryloyl "head" group at one end, and a terminal hydroxyl (OH) group at the other end, essentially quantitatively, producing an insignificant proportion of diacrylate (for example, ethylene glycol dimethacrylate) due to interesterification, and essentially without producing cyclic oligomers. Hereinafter the acryloyl and methacryloyl "head" groups are together referred to as "(meth)acryloyl" groups, and the alcohol used is referred to as a "hydroxyalkyl (meth)acrylate", for convenience and brevity.
The macromer of (meth)acryloyl headed polylactone so formed may be used to initiate block copolymerization with a ring-openable ether, using the same catalyst, yielding a macromer of block copolymer in which the polylactone block is adjacent the terminal double bond, and the OH group is attached to the end of the polyether chain.
This macromer of polylactone-b-polyether block copolymer (structure II herebelow) is then copolymerizable through its head group with an olefinically unsaturated copolymerizable monomer. The copolymerization of the macromer of block copolymer with one or more conventional olefinic monomers generates a "polymacromer" with a saturated hydrocarbon backbone having polylactone-b-polyether branches thus resulting in a graft or comb copolymer in which the polyether blocks are farthest from the backbone. Such copolymerization of the macromer of block copolymer to form comb copolymers, differs from graft copolymerization, in the sequence of formation of the backbone relative to the formation of the graft unit.
In my copending parent application I disclosed the formation of (meth)acryloyl headed macromers of polylactone which always had a polyether spacer, the polylactone chain being intermediate the polyether spacer and the OH propagating group. At the time, it appeared that the presence of the polyether spacer ahead of (that is, preceding) the polylactone chain at the tail end of the macromer was responsible for the substantial absence of diacrylate, and cyclic oligomers in the macromer product. The macromer product had the structure ##STR1## wherein, the O of the OH group is contributed by the last repeating unit of the polyether;
R.sup.2 is H or C.sub.1 -C.sub.20 alkyl, preferably lower C.sub.1 -C.sub.5 alkyl, and most preferably methyl; PA1 R.sup.3 is selected from a saturated group consisting of branched or linear alkylene, haloalkylene, alkoxyl, haloalkoxyl, each C.sub.1 -C.sub.20, aralkylene, haloaralkylene, aralkoxyl, and haloaralkoxyl, each C.sub.7 -C.sub.20 ; PA1 (PolyLact) represents a chain of lactone units; and, PA1 (PolyEt) represents a polyether block containing no active hydrogen, i.e. no hydrogen attached to oxygen, nitrogen, or sulfur, and has a number average molecular weight Mn up to about 30,000. PA1 (B) an ethylenically unsaturated primary or secondary (meth)acryloyl alcohol wherein the ethylenic unsaturation is adjacent a carbonyl group as in the structure ##STR3## wherein R.sup.2 and R.sup.3 have the connotation hereinabove; and, (C) an oxonium salt cationic initiator while maintaining a temperature in the range from about 10.degree. C. to about 80.degree. C.; so as to produce a polylactone macromer substantially free from di(meth)acrylic species, said macromer having the structure EQU R--(M).sub.m --OH (LM) PA1 n" represents an integer in the range from 1 to about 10.sup.5, more preferably 1-10.sup.4 ; and, (b) the macromer block copolymer with an olefinically unsaturated monomer so as to have the structure ##STR7##
I now know that the highly specific polymerization which yields the substantially diacrylate-free, and cyclic oligomer-free product, essentially quantitatively, is the result of operation at relatively low temperature; and these unexpected results are uniquely derived from the characteristics of the trialkyloxonium (TAO) salt (cationic initiator) I used. By "substantially diacrylate-free" I refer to a macromer product having less than 0.05 percent by weight (% by wt) diacrylate.
This was particularly unexpected because a strong catalyst such as TAO is known to be undesirable for such formation of a macromer of polylactone due to the promotion of deleterious interesterification. More surprising is that the same TAO catalyst may then be used to prepare a macromer of block copolymer, in which the polylactone is blocked to a polyether. Again, this polymerization occurs without the formation of a significant proportion of diacrylic polymer.
The macromer is formed in commercially acceptable yield by the cationic ring-opening polymerization of a lactone in conjunction with (a) a hydroxyalkyl (meth)acrylate (or `propagator`) which functions as the generator of the propagating species (the OH group), and (b) an oxonium salt cationic ring-opening catalyst which has been found uniquely effective at so low a temperature that there is essentially no formation of byproducts, particularly diacrylic species.
U.S. Pat. Nos. 4,281,172 and 4,340,497 to Knopf, and 4,632,975 to Cornell, teach the preparation of macromers of polylactones by end-capping reactions which are known to be notoriously non-quantitative.
U.S. Pat. No. 3,655,631 to Fraser, teaches that lactones are polymerized in the presence of an ethylenically unsaturated amide or ester with a strong organic acid such as halogen activated carboxylic acids or sulfonic acids as catalyst, and a compound having the formula L-CH.sub.2 OH as initiator, wherein L contains ethylenic unsaturation activated by amide or ester linkages, the ethylenic unsaturation being either CH.sub.2 .dbd.CH&lt; or CH.sub.2 .dbd.CH--. The acid has a pK value of less than 3 in water at 25.degree. C. An acrylic group was exemplified, but the determination of unsaturation of the (meth)acrylic groups by the iodine method is undesirable, and unreliable, hence of questionable probative value. I have been unable to determine unsaturation of the (meth)acrylic groups by the iodine method. Further, as stated in U.S. Pat. Nos. 4,6813,287 and 4,504,635, the macromers prepared according to Fraser's method necessarily contain a large amount of residual acid catalyst. The presence of such acaid catalyst in the product likely produces degradation and decrease of shelf life or pot life of coating systems produced from the macromer.
In the '365 patent to Fraser, the resulting terminally unsaturated polylactones were copolymerized with an ethylenically unsaturated monomer, for example, vinyl acetate; and, were used as plasticizer for poly(vinyl chloride) (PVC). But the teaching as to any ethylenically unsaturated group is not as broadly applicable as at first appears. For example, when the ethylenically unsaturated group is a vinyl ether group, the alkenyl alcohol, such as 2-hydroxyether vinyl ether (CH.sub.2 .dbd.CH--O--CH.sub.2 --CH.sub.2 OH) or 4-hydroxybutyl vinyl ether, is an ineffective propagator. The vinyl ether group of the alkenyl alcohol does not survive under the conditions of cationic ring-opening polymerization of lactones and undergo carbocationic polymerization. As a result, the lactone polymers do not have an ethylenically unsaturated head group.
Further, since Fraser was unaware that the OH group could function as the propagating species, he attributed his polymerization to the ester or amide linkage of the alcohol. Thus, the possibility of using the polylactone polymer he made, to initiate a block polymerization with a polyether could not have occurred to him, even if he was prepared to use a different catalyst to do so. Still further, it is only because it is now known that the same lactone ring-opening catalysts are uniquely effective in the ring-opening polymerization of alkylene oxides, was it possible to arrive at the concept of using an --OH terminated polylactone with an ethylenically unsaturated head group, as the propagator for the formation of a macromer of polylactone-b-polether macromer, which, in turn, could then be copolymerized with a copolymerizable monoolefinically unsaturated monomer.
The significance of low temperature operation can best be appreciated by noting the uniformly high temperatures used for lactone polymerization in the prior art. Thus, U.S. Pat. No. 4,188,472 to Chang, discloses the polymerization of lactone in the presence of hydroxyalkyl (meth)acrylate with tetrabutyl titanate as the catalyst at 130.degree. C.
U.S. Pat. No. 4,368,320 to Aldinger, discloses the polymerization of lactone in the presence of hydroxyalkyl (meth)acrylate with dialkyl tin oxide or glycolate at a temperature of from about 110.degree. C. to about 125.degree. C.
To cope with the problem of residual catalyst and minimize its effect, U.S. Pat. Nos. 4,504,635 and 4,6833,287 to Weber, Jr. and Koleske, respectively, disclose the polymerization of lactone in the presence of hydroxyalkyl (meth)acrylate with less than 200 ppm of catalyst. Preferred catalysts are stannous octoate, dibutyl tin dilaurate, and other tin compounds; also, alkyl titanates such as butyl titanate. But the reaction has to be carried at a temperature in the range from about 100.degree. C. to about 140.degree. C., and though less than 2% by wt of diacrylate is said to be formed, no mention is made as to how this level of diacrylate was determined.
UK Patent Application GB No. 2,101,121A to Okitsu and Watanabe discusses numerous attempts to polymerize a lactone and obtain a polylactone-modified acrylic polyol.
Particularly decrying the use of organotin or organotitanate catalyst because of the per se polymerization of the acrylic ester at the minimum 130.degree. C. required, they teach the polymerization of lactone in the presence of hydroxyalkyl (meth)acrylate with stannous halide at a temperature as low as 80.degree. C.-130.degree. C. with only a small amount (100 ppm) of catalyst, resulting in only slight formation of the diacrylate, and little interesterification reaction. Though advocating the use of a reaction temperature at the low end of the range, they provide examples only at 120.degree. C. Despite this relatively high temperature, the rate of reaction is so slow that the fastest reaction requires 8 hr (hours).
It is known that oxonium salts are effective in ring-opening polymerization of oxirane compounds (see U.S. Pat. No. Re 31,577 to Riew); and that a hydroxyalkylacrylate provides a vinyl functional head group in such a polymerization (see U.S. Pat. No. Re 31,468). It so happens that triethyloxonium hexachloroantimonate and triethyloxonium tetrafluroborate are known to be effective in the polymerization of lactones (see "Catalytic Polymerization of epsilon-caprolactone" by Burba, C et al Ger. Offen. DE No. 2123968) but not for providing an unsaturated head group. Since it is critically important that my macromer possess the (meth)acrylyl head group, the possibility of using an oxonium salt in conjunction with the hydroxyalkyl(meth)acrylate propagator was given little weight. Also, it is well known that, because the mechanisms are generally different, an effective catalyst for cationic ring-opening an oxirane to form a polyether, is not likely to be effective for ring-opening a lactone to form a polyester, and vice versa. It was simply the availability of the particular catalysts which instigated the investigation of their activity in conjunction with a hydroxyalkyl-(meth)acrylate propagator which initiated the ring-opening polymerization of lactones, and such activity fortuitously was found to be high.
It is to be noted that the macromers of this invention are formed by cationic ring-opening and not carbocationic polymerization, though both are classified as cationic polymerizations and may even use the same cationic initiator. The cationic ring-opening of a lactone involves the opening of strained rings of cyclic monomers and the propagating species is an acyl carbonium ion; carbocationic polymerization involves substituted olefinic monomers where the propagating species is a carbenium ion.